A BTR-80 swimming ashore from a tank landing ship

Bridging the Gap: Warsaw Pact River Crossing

During the Cold War, the Warsaw Pact armies studied the disposition of rivers in western Europe. It concluded that they would have to cross water obstacles up to 100m wide every 35 to 60km. Every 100-150km, they would encounter a water obstacle between 100m and 300m wide. Every 250-300km they would encounter one that was wider still. In a war in western Europe, the Warsaw Pact armies expected to advance an average of 100km per day, leading to a significant number of river crossings. Since there was no guarantee of securing bridges intact, the Warsaw Pact put a great deal of emphasis on their ability to cross water obstacles. A range of equipment was created to bridge gaps or ferry vehicles over rivers. Echographs were developed, that could quickly measure water depth and river width. Many light armoured vehicles could swim. Main battle tanks carried snorkels that allowed them to wade through water up to 5m deep.

A snorkelling T-72 coming out of the water
A snorkelling T-72 coming out of the water

Snorkelling

It seems likely that the armies of the Warsaw Pact preferred not to snorkel main battle tanks, and that ferries or pontoon bridges were preferred. None the less, a 1971 British Army intelligence report stated that the Soviet army considered it “a practical operation of war” (Army Technical Intelligence Review, April 1971). Every tank crew was fully trained in snorkelling. Training took place on purpose-built sites, with good facilities. Emphasis was placed on giving the crew confidence in their ability to snorkel well and safely. 

Training was split into two phases. The first phase, lasting up to two months, concentrated on preparing the crews to operate tanks under water. Training covered swimming, diving, carrying out procedures underwater whilst wearing escape masks. There was a good deal of safety training, which helped with crew confidence and morale. Rescue operations were practised on simulators. Crews were not allowed to move onto the second phase until they had passed the first phase.

In the second phase of training, the crew got the chance to put their skills to the test. A five-meter deep lake would be used to practice driving underwater. Initially, drivers would drive 90m underwater, progressing to 150m as their skills improved. At least some sites also had facilities for blind driving, with the driver guided only by the tank’s gyro compass. After passing this second phase of training, crews would join their units.

Sealing and preparing a tank for snorkelling could take as little as 15 minutes. Older tanks took longer, up to half an hour. This would be done in a concealed area 3-5km from the river. When the tanks got to within 1-2km of the river, snorkels would be fitted. Tanks crossed at slow speed, in a column formation, with a 30m gap between vehicles. Drivers would not change gear or stop while in the water. Once across, the tank would have to stop while the crew removed the waterproofing. Until this was done, the turret could not be traversed or the gun fired. If a tank stalled in the river, the crew would flood it before escaping through the hatches.

An alternative method of snorkelling was to use winches to pull unmanned tanks across. A pair of armoured recovery vehicles would set up on the far bank with a pulley block and anchoring unit. Up to three tanks could be pulled across the river simultaneously. Using this method, 10-tank company could cross a 200m wide river in 35 minutes, assuming the tanks had already been sealed. The crews would cross separately, in amphibious vehicles such as APCs, or on boats.

Snorkelling was not to be carried out under fire, and in some cases, simply wouldn’t be possible. The entry bank had to be less than 25º, the exit bank less than 15º, and the current no more than three metres per second. In winter, drifting ice could damage the snorkel. The river bottom had to be reasonably firm, and free of boulders and craters.

Swimming

Many lighter AFVs were amphibious, and could swim across water obstacles. All APCs from the BTR-50 onwards, and all IFVs, were fully amphibious. The BRDM series of reconnaissance vehicles, and even some self-propelled artillery and AA vehicles could swim. Most of these were propelled in the water by their tracks, although some used water jets, which gave a better performance in the water. 

A BTR-80 swimming ashore from a tank landing ship
A BTR-80 swimming ashore from a tank landing ship

Water obstacles would only be crossed under fire as a last resort. In these cases, a great deal of artillery would be called upon to support the operation. If at all possible, helicopter troops would be landed on the far bank, and attack simultaneously with the crossing. Tanks would stay on the near bank to provide covering fire, while amphibious armoured vehicles swam across. Once a bridgehead was established, tanks and other vehicles would snorkel or be ferried across. These would then continue the advance, while engineers worked to build more permanent bridge crossings over the obstacle.

Armoured Bridgelayers

Soviet estimates found that two-thirds of the river obstacles they would encounter in Europe were less than 20m wide. This led to the development of vehicle-launched bridges capable of quickly crossing these gaps. The Polish army developed a tracked bridge, which was pushed into place by a tank. Small numbers of a T-34 based bridging tank were delivered to the Soviet army in 1957. This was soon superseded by the MTU-54, also sometimes referred to as the MTU or MTU-1. 

MTU-54

In 1955, the MTU-54, a bridge layer based on a T-54 chassis, was introduced. The MTU-54 mounted a simple 12.3m bridge, carried horizontally on top of the vehicle. Unlike later vehicles, the bridge was not folded for transit. A chain drive mechanism moved the bridge forwards to launch, before being lowered into place. This method had the advantage of keeping the silhouette low whilst launching the bridge. The MTU-54 could bridge an 11m gap, and had a load capacity of 50 tonnes. Launch time was three to five minutes, and recovery can take place from either end.

An MTU-54 showing the simple bridge
An MTU-54 showing the simple bridge

Unusually, it was fitted with a DShKM machine gun, mounted in the centre of the vehicle. This had to be removed before launching the bridge. Later vehicles were fitted with a deep wading snorkel, NBC protection, and automatic fire supression system.

MTU-20

From 1967, the MTU-20 became the primary Soviet tank-launched bridge. This mounted a bridge on a T-55 chassis. In order to allow a longer span length whilst maintaining a low silhouette when launching, the ends of the bridge folded back when in transit. When launching the bridge, a stabiliser at the front was lowered. The ends of the bridge were then unfolded and the bridge rolled forward, before being lowered into place. The MTU-20 had a span length of 20m, with a load capacity of 60 tonnes. Launching the bridge took five minutes, recovery from either end took between five and seven minutes. Both launching and recovery could be carried out while the crew remained inside the vehicle. It was fitted with a deep wading snorkel, NBC protection, and automatic fire supression system. 

BLG-60 (Poland/DDR)

The non-Soviet Warsaw Pact armies showed a preference for the more common scissor bridge design. Poland and East Germany jointly developed the BLG-60, which mounted a 50 tonne, 21.6m scissor bridge on a T-55 chassis. The bridge was launched by being lifted up to the vertical, then unfolded and lowered over the gap. This design gave a quicker launch time than the Soviet designs, at the expense of a very high silhouette during launch. The BLG-60 was fitted with NBC protection and a deep-wading snorkel. An improved version, the BLG-67, was introduced in the late 1970s. 

MT-55A (Czechoslovakia)

Czechoslovakia also built its own bridge layer, the MT-55A. Like the BLG-60, this mounted a scissor bridge on a T-55 chassis. A front spade stopped the vehicle being tipped over by the weight of the bridge. Launch time was two to three minutes, recovery time five to six minutes. Both tasks could be carried out from inside the vehicle. It could span an obstacle of up to 18m, and load capacity was 50 tonnes. It had a gap measuring device and inclinometer to help with finding a suitable site for the bridge. Other equipment included infra-red night vision equipment, snorkel, automatic fire extinguisher, and NBC protection. Unusually, the Soviet army adopted the MT-55A, albeit in small numbers. 

Initially, the scissor bridge carried by the MT-55A had circular holes in the sides of the bridge. Later models had solid sides. Multiple bridges could be combined to span larger gaps. 

MTU-72

In 1974, a new bridge layer entered service, the MTU-72. These were made from existing T-72 tanks with the turret replaced with a bridge-launching mechanism. The bridge was of cantilever design, similar to that on the MTU-20, but made of an aliminium alloy. The 20m bridge had a load capacity of 50 tonnes and could span a gap of up to 18m. A second bridge could be launched from the first one to span a gap of up to 35m. Launching the bridge took three minutes, recovery eight minutes. Both launching and recovery could be carried out while the crew remained inside the vehicle.

An MTU-72 at Russia Arms Expo 2013, showing the unusual bridge design
An MTU-72 at Russia Arms Expo 2013, showing the unusual bridge design (CC-BY-SA 3.0, by Vitaly V. Kuzmin)

A blade is fitted to the front of the hull, which is primarily intended to stabilise the vehicle during launching and recovery. It can also be used as a bulldozer blade. A deep wading snorkel, NBC protection system, fire suppression system, and thermal smoke generation unit are also fitted. 

Amphibians & Ferries

K-61

The K-61 tracked amphibious ferry was introduced in 1950, a direct result of wartime experience with DUKW amphibious lorries supplied by the USA. It remained in Soviet service until the late 1960s. It was fully tracked, and based on a light AFV chassis, but was not armoured. The K-61 could carry eight wounded on stretchers, 40 fully-armed infantry, up to five tonnes of equipment, a lorry up to 2.5 tonnes, or an artillery piece.

Loading is done via ramps at the rear. Vehicles can be simply driven on, and a winch is provided for loading heavy equipment such as artillery pieces. It is driven through the water by a pair of propellers, at a speed of up to 10km/hour.

PTS-M

The PTS-M was introduced in 1966, as a replacement for the K-61. Larger than the K-61, it also had an amphibious trailer, although this was found to be of little use except in very calm waters. A more powerful engine meant that it could carry a greater load, 7.5 tonnes on land and 15 tonnes on water. Rear ramps are used to load cargo, with a winch for loading heavy non-motorised loads. An infra-red searchlight and infra-red driving lights were fitted. 

PTS-2

The PTS-2 was a much improved and modernised version of the PTS-M, introduced in the late 1970s. It had a new suspension, derived from the MT-T artillery tractor. A pair of propellers drive the vehicle in the water. Load was the same as the PTS-M. The cab is fitted with NBC protection. 

GSP

The GSP heavy amphibious ferry was introduced in 1959. A single ferry was made up of two distinct units, one left and one right. The two units were mirror images of each other, and not interchangeable. Before entering the water, a trim vane was erected at the front of the hull. The two units then entered the water separately and linked up. Once linked, the pontoons, which were inverted while in transit, were swung upright, and the treadways deployed. It was important that the pontoons were both unfolded together, to avoid overbalancing the whole. Assembly time was 6-10 minutes. 

A diagram showing how two GSP vehicles were mated to create a ferry
A diagram showing how two GSP vehicles were mated to create a ferry

The ferry had hydraulically operated ramps at each end, allowing vehicles to be driven on at one end and off at the other. Maximum capacity was 52 tonnes, enough to carry a main battle tank. It was reported that tanks could fire their main armament whilst on the ferry, in good conditions.

The vehicle itself was tracked, with a suspension similar to the PT-76 light tank. It had infra-red driving lights, although these were only for use on land. The hull and pontoon was lightweight steel filled with plastic foam. The foam increased bouyancy and reduced vulnerability to enemy fire. Propulsion in the water was provided by four propellers (two per vehicle), mounted in tunnels under the hull. Maximum speed in the water was 8km/hour.

PMM-2

Initially known to NATO as the ABS(T), the PMM-2 was introduced in 1974 as a replacement for the GSP ferry, and possibly the PMP pontoon bridge. It is based on a BAZ-5937 chassis. Two aluminium folded pontoons are mounted on top, with entrance ramps. As the vehicle enters the water, the pontoons are hydraulically unfolded to either side of the vehicle, with the vehicle itself forming a centre section. It is propelled in the water by water jets. 

As a ferry, units can be used individually (40 tonne capacity), in pairs (80 tonne capacity), or in threes (120 tonne capacity). A single vehicle can be used as a bridge, to span gaps of up to 17m. Up to ten vehicles can be combined to span larger gaps, with no need for bridging boats.

Tactics

Most river crossings would have been assault crossings from the march, at sites that were only lightly defended, if at all. Reconnaissance patrols of up to platoon size, operating up to 50km ahead of the main body and equipped with specialised equipment, would find suitable sites. When a crossing site had been selected, a forward detachment, two to three hours ahead of the main body and avoiding contact with the enemy, would secure the site. A typical forward detachment would consist of a motor rifle battalion with an attached tank company and artillery battalion. Amphibians, ferries, air defence, anti-tank and chemical defence units would also be attached. Heliborne or occassionally airborne troops could also be used in this role.

If the crossing site was defended, the attack would be carried out with significant artillery and air support. River crossings got priority for air support, and were considered particularly vulnerable to enemy air attack. Air defence assets would be deployed close to the crossing site, and would cross the river as soon as feasible to extend their coverage.

The crossing itself would be carried out by APCs or IFVs swimming across the river, supported by tank and artillery fire from the near shore. A few tanks may have crossed in the first wave, but most would provide fire from the near bank and cross later. Artillery and anti-tank units would cross immediately after the infantry to provide support in holding the bridgehead. Tanks would cross using ferries, snorkelling, or bridges.

Conclusion

In the event of war in Western Europe, the Warsaw Pact expected their armies to advance quickly. The rivers of West Germany could not be allowed to slow the advance, and so considerable effort was put into developing equipment for their engineers. This equipment was simple, rugged, and supplied in significant quantities. Both peacetime exercises and experience in Afghanistan demonstrated that Soviet combat engineers were an effective force.